U.S. patent number 4,517,505 [Application Number 06/463,456] was granted by the patent office on 1985-05-14 for varible force, eddy-current or magnetic damper.
This patent grant is currently assigned to The United States of America as represented by the Administrator of the. Invention is credited to Robert E. Cunningham.
United States Patent |
4,517,505 |
Cunningham |
May 14, 1985 |
Varible force, eddy-current or magnetic damper
Abstract
An object of the invention is to provide variable damping for
resonant vibrations which may occur at different rotational speeds
in the range of rpms in which a rotating machine is operated. A
variable force damper in accordance with the invention includes a
rotating mass (12) carried on a shaft (11) which is supported by a
bearing (13) in a resilient cage (14). Cage (14) is attached to a
support plate (15) whose rim extends into an annular groove in a
housing (17). Variable damping is effected by tabs (18) of
electrically conducting, non-magnetic material which extend
radially from the cage (14). The tabs (18) at an index position lie
between the pole faces of respective C-shaped magnets (19). The
magnets (19) are attached by cantilever spring members (20) to the
housing (17). By rotating the support plate (15) about the axis of
shaft (11), the tabs (18) may be rotated through an angle 0 of
about 40.degree. away from the index or 0.degree. position. At the
40.degree. position minimum damping is obtained. To position
support plate (15) to achieve a desired amount of damping, means
for generating an electrical signal indicative of the vibrating
displacement of shaft (11) such as displacement detector (29) and
correction module (28) to control a servo (27). The servo (27) can
drive the support plate (15) through various means such as gears,
drive wheels or the like.
Inventors: |
Cunningham; Robert E.
(Cleveland, OH) |
Assignee: |
The United States of America as
represented by the Administrator of the (Washington,
DC)
|
Family
ID: |
23840147 |
Appl.
No.: |
06/463,456 |
Filed: |
February 3, 1983 |
Current U.S.
Class: |
318/611; 310/93;
335/100; 310/77 |
Current CPC
Class: |
F16C
27/04 (20130101); F16F 15/03 (20130101); F16C
2360/00 (20130101) |
Current International
Class: |
F16F
15/03 (20060101); F16C 39/00 (20060101); F16C
39/06 (20060101); G05B 005/01 () |
Field of
Search: |
;318/611-614,460
;310/77,93,105-110 ;324/125 ;335/100 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dobeck; B.
Attorney, Agent or Firm: Musial; Norman T. Manning; John R.
Mackin; James A.
Government Interests
ORIGIN OF THE INVENTION
The invention described herein was made by an employee of the
United States Government and may be manufactured or used by or for
the Government for governmental purposes without the payment of any
royalties thereon or therefor.
Claims
I claim:
1. A variable damper for substantially eliminating resonant
vibrations in a rotating mass carried on a shaft in a housing and
wherein the shaft is provided with at least one bearing, said
damper comprising:
a resilient support for said bearing, said support being rotatable
about the axis of rotation of said shaft;
a carrier plate for said bearing support comprising a rotatable
plate, said bearing support being attached to said carrier plate
for rotation therewith;
a plurality of tabs extending radially from said bearing support,
said tabs being of electrically conductive, non-magnetic
material;
a plurality of magnets equal in number to said plurality of tabs,
each magnet having at least one pole face in non-contacting,
maximum surface-to-surface confrontation with a respective tab when
said plate is in a 0.degree. index position; and
means for rotating said carrier plate whereby said tabs may be
positioned from the 0.degree. index position to one in which there
is minimum surface-to-surface confrontation between the tabs and
respective magnets.
2. The damper of claim 1 wherein a cryogenic liquid is applied to
said tabs and magnets.
3. The damper of claim 1 wherein said bearing support is a squirrel
cage spring.
4. The damper of claim 1 wherein said magnets are C-shaped with
each tab lying between the poles of a respective magnet when said
carrier is in said 0.degree. index position.
5. The damper of claim 4 wherein each pole of the C-shaped magnets
is provided with a rare earth metal pole face.
6. The damper of claim 1 wherein each magnet is resiliently
supported on said housing.
7. The damper of claim 1 and including an adjusting shaft carrying
a drive wheel engaging said carrier plate to rotate the same, when
said shaft is turned.
8. The damper of claim 7 and including:
means for generating a first electrical signal indicative of radial
displacement of said rotating mass;
servo means drivingly connected to said adjusting shaft; and
means for adjusting said first electrical signal and directing it
to said servo whereby said carrier plate is rotated to a prescribed
position in accordance with the resonant vibrations of said
rotating mass.
9. The damper of claim 1 wherein said tabs are of a material
selected from the group of metals comprising copper and
aluminum.
10. The damper of claim 1 wherein said magnets are electromagnets
with a predetermined, constant field strength.
11. The damper of claim 1 and including:
first means for generating an electrical signal related to the
rotational speed of said rotating mass;
second means for rotating said carrier plate between a 0.degree.
index position which provides maximum damping and a position which
provides minimum damping, and;
third means for transmitting said signal from said first means to
said second means whereby said carrier plate is automatically
positioned to provide predetermined damping at a plurality of
specific rotational speeds of said rotating mass.
12. The damper of claim 11 wherein said second means comprises a
servo driving a wheel which engages a rim portion of said carrier
plate.
Description
DESCRIPTION
1. Technical Field
The invention relates to high speed rotating machinery and is
directed more particularly to damping apparatus for reducing
resonant vibrations of the rotating parts.
With any rotating machinery there is one or more rotating speeds at
which the rotating body will develop resonant vibrations. These
vibrations cause stress on support bearings and the shaft
supporting the rotating mass and will cause early destruction of
these components. Examples of high speed, turbomachinery are the
fuel and oxidizer pumps used on the main engines of a NASA space
shuttle. These pumps are used for liquid oxygen and liquid
hydrogen. Such machines have very high power to weight ratios and
are required to operate at rotor speeds of up to 36,000 rpm.
In accelerating up to operating speed, it is common to encounter
one or more system resonant frequencies. A capability of varying
the stiffness and damping of shaft bearing supports while operating
through such resonant frequencies is an important goal. Having this
capability can reduce the magnitude of the forces transmitted to
the bearings and seals and can, therefore, prolong their life or
possibly prevent sudden and catastrophic failure.
2. Background Art
In the prior art damping of rotating machinery has been attempted
by a number of different devices. In one such device, the shaft
bearings are supported in resilient materials or by springs having
predetermined spring rates.
In turbomachines such as turbojet engines, radial and axial
compressors, and high speed gas liquefiers, fluid film dampers are
often used. These dampers employ a viscous fluid film between
moving parts. Vibrational energy induced in the rotor and
transmitted to the bearing supports is dissipated as heat in
shearing the viscous fluid.
The so-called squeeze film damper dissipates energy by pumping a
viscous fluid in and out of a narrow annulus. The amount of damping
and stiffness is determined by the original design and expected
amplitudes of vibration. The squeeze film type dampers normally
must be located very close to a bearing where lubricating oils are
available in large quantities, thus creating a design problem.
Another type of damper commonly used is a friction or coulomb
damper. In this type damper the energy dissipated is dependent on
the coefficient of friction of two contacting surfaces under
applied pressure. The problem here is to predict the amount of
damping and stiffness available for any given vibrational
situation. If the contacting surfaces are under too little
pressure, slip relative to one another may produce erratic amounts
of damping. Conversely, if the pressure is too great, the
contacting surfaces may have little, if any, slip resulting in high
stiffness values and little, if any, damping.
U.S. Pat. No. 3,316,661 to Simpson et al discloses an eddy current
brake in which a movable shield or shunt is interposed between a
magnet and a rotating conductor. The shunt may be moved through the
gap between the magnet and the rotating conductor to shield
variable portions of the conductor from the magnetic field to alter
the area and shape of the magnetic field penetrating the disc.
U.S. Pat. No. 3,601,641 to Baermann discloses an eddy current
and/or induction break or clutch comprised of a breaking inductor
and a ferromagnetic eddy current conductor arranged for relative
rotation with respect to one another. The magnetic field produced
by the permanent magnet 38 can be increased or decreased by the
electromagnetic field produced by a field winding. Breaking torque
can be adjusted by changing the energizing field of the AC
generator which feeds the windings.
U.S. Pat. No. 4,198,863 to Bartek discloses an electromagnetic
torsion stiffness arrangement having a conductor located on a disc
rotating in an air gap between magnetic systems. The disc also
serves to dampen the rotary motion.
U.S. Pat. No. 3,510,705 to O'Neill et al discloses a magnetic
hysteresis device having a magnetic hysteresis member and at least
one magnetizing head supported for relative movement in such a way
that energy is dissipated within the member by magnetic hysteresis
to produce a hysteresis drag force opposing the relative movement.
The hysteresis drag force may be varied in accordance with a
predetermined function of the relative displacement of the member
and head.
U.S. Pat. No. 3,637,169 to Tossman et al discloses a pendulum
having a vane member formed of electrically conductive, nonmagnetic
material which swings between pole faces of a magnetic structure
and creates eddy current losses within the vane member to dissipate
coulombic energy.
U.S. Pat. No. 4,200,003 to Miller discloses a rotary disc damper
using magnetic fluid as the damping medium. The damper comprises a
permanent magnet rotor enclosed in a magnetically permeable
housing. The housing contains a magnetic fluid which is held in
place by the magnetic forces generated by the magnet rotor. The
torque of the damper may be varied by changing the viscosity of the
magnetic fluid or the level of the magnetic flux in the magnetic
circuit.
DISCLOSURE OF THE INVENTION
According to the invention, one end of a shaft carrying a rotating
mass is supported by a suitable bearing which, in turn, is
supported resiliently in a cage member. The cage member is attached
to a plate which may be rotated to position electrically
conductive, non-magnetic tabs which extend radially from the cage
member.
At an index position of the support plate each tab lies within the
pole faces of a respective C-shaped magnet. Each magnet is
supported by a cantilever spring from a housing in which the
support plate is free to rotate.
Maximum damping of shaft vibrations is achieved when the tabs are
positioned within the pole faces of their respective magnets. By
rotating the support plate, the cage member with the attached tabs
can be rotated through an angle of approximately 40.degree. to
achieve minimum damping effect.
Electronic circuitry may be provided to measure the displacement or
speed of the rotating shaft. A signal representative of these
parameters may be modified and amplified to drive a servo which
rotates the support plate to a position which will achieve the
desired damping for a particular frequency or speed of
rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a transverse cross-sectional view of a variable force,
eddy current or magnetic damper embodying the invention.
FIG. 2 is a cross-sectional view taken along the lines 2--2 of FIG.
1.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown a variable force,
eddycurrent damper 10 constructed in accordance with the invention.
A shaft 11 carries a mass 12 such as a turbine which rotates with
the shaft 11.
One end of the shaft 11 is journaled in a bearing 13 which is
disposed in one end of a bearing support such as a squirrel cage
spring 14. The other end of the squirrel cage spring 14 is attached
to the center of a bearing support carrier plate 15 which has a
circular rim.
The shaft 11 extends through an aperture 16 in the spring carrier
15 and coaxially through the squirrel cage spring 14. Spring
carrier plate 15 is rotatably supported by an annular groove in a
housing 17 in which the eddy current damper 10 is disposed.
To the end that resonant vibrations of the shaft 11 and rotating
mass 12 will be adequately damped, tabs 18 of highly electrically
conductive, non-magnetic material are attached to and extend
radially from the squirrel cage spring 14 adjacent the bearing 13.
When the spring carrier 15 is at 0.degree. index position, as will
be described presently with regarding to FIG. 2, each tab 18 is
positioned between the poles of a respective C-shaped magnet
19.
Each C-shaped magnet 19 is supported by a cantilever spring 20 from
the housing 17. The C-shaped magnets 19 are provided with rare
earth magnetic pole faces 21 to increase the magnetic strength
applied to the tabs 18.
Referring now to FIG. 2, there is shown a transverse sectional view
taken along the line 2--2 of FIG. 1. The tab 18 on the left as
viewed in FIG. 2 is aligned with line 22 at a 0.degree. index
position when it is in maximum surface-to-surface confrontation
between the pole faces of its respective C-shaped magnet 19.
Similarly, at the 0.degree. position of spring carrier 15, all of
the remaining tabs will be positioned between the pole faces of
their respective C-shaped magnets 19. At the 0.degree. position of
the spring carrier 15, maximum damping effect is obtained. By
rotating the spring carrier 15 through an angle .phi. of 40.degree.
to a position, as indicated by line 23, substantially zero damping
is effected.
In order to rotate the spring carrier 15 to a desired position or
angle .phi. whereby the tabs 18 are positioned as desired, a tab
positioner 24 is provided as illustrated in FIG. 1. Tab positioner
24 includes a wheel or gear 25 carried on a shaft 26. The wheel 25
engages the rim of the spring carrier plate 15 so that by rotating
the shaft 26 some predetermined number of turns, plate 15 will be
rotated, thereby positioning the tabs 18 as desired.
In order that the spring carrier may be automatically rotated to a
prescribed damping position, shaft 26 of the tab positioner 24 may
be rotated by a servo 27. Servo 27 is supplied with a correction
signal from a correction module 28 in response to radial movement
of the rotating mass 12 as measured by a displacement detector
29.
Displacement detector 29 may be any one of well known types
operating on capacitive, inductive or light beam principles. The
signal generated by the displacement detector 29 is related to the
radial displacement of the rotating mass 12 and after being
amplified and/or modified by the correction module 28, drives the
servo 27.
Rotation of the carrier plate 15 can also be accomplished by
directing to the servo 27 a signal related to the rotating speed
(rpm) of the mass 12 so that at certain rpms plate 15 rotates to
place the tabs 18 at predetermined positions. These positions may
be determined empirically by rotating mass 12 at various speeds and
determining the rpm's at which unacceptable resonant vibrations
occur. Plate 15 is then rotated to provide maximum damping for each
particular rpm at which the resonant vibrations occur. When these
factors are known, an rpm counter for the mass 12 can signal servo
27 to adjust the plate 15 for maximum damping.
As discussed previously, one particular application of the
above-described invention is in pumps operating in cryogenic
environments such as liquid hydrogen. Advantageously, cryogenic
temperatures increase the conductivity of the tabs 18 and,
consequently, increase the damping effectiveness of the eddy
current shaft damper described above. Tests have shown that the
damping provided when tabs 18 are aluminum and the apparatus is
immersed in liquid nitrogen is seven times greater than when the
tabs 18 are at room temperature.
Theoretically, if tabs 18 are copper the damping effect should be
11 times greater in liquid nitrogen than at room temperature. With
a low purity copper material, however, the damping in liquid
nitrogen was only 21/2 times as great as at room temperature. With
all conditions being the same, copper, because of its high
conductivity, has greater damping effect than aluminum.
While the variable force damper shown in FIG. 2 utilizes permanent
magnet 20, it will be understood that electromagnets can also be
used. Also, while four tabs 18 are shown, three tabs with
associated magnets may be used as well as five or more tabs with
associated magnets. Of course, less damping is effected with three
tabs while more than four tabs add to the weight and complexity of
the damping apparatus without proportionately increasing the
damping effect.
It will be understood that changes and modifications may be made to
the above-described invention without departing from its spirit and
scope as set forth in the claims appended hereto.
* * * * *